Cotton fabrics are bleached prior to dyeing and finishing to remove natural pigment impurities from cotton fibers. The conventional bleaching process of cotton fabrics is usually performed with hydrogen peroxide (H2O2) as an oxidant at high temperature (>95° C.) and alkaline (˜pH 11) conditions, which has the disadvantages of high energy consumption, heavy waste water treatment burden and severe fiber damage.
It has been reported that the bleach activator N-[4-(trialkylammoniummethylene)benzoyl]lactam chloride (TBLC) can react with H2O2 in a near-neutral water solution to form a more active 4-(trialkylammoniummethylene)peroxybenzoic acid in situ, which enables cotton fabrics to obtain a better bleaching effect at a low temperature and the pH close to 7, and to obtain good whiteness. In long-term practice, application of the TBLC-activated hydrogen peroxide bleaching system in a thermal bleaching process has gradually matured, and the performance of the fabric has been able to meet the corresponding requirements. The cold pad-batch process has many advantages such as low energy consumption, low water consumption, high flexible productivity, high process adaptability and small loss of fabric strength. However, when TBCC/H2O2 is applied to a cold pad-batch bleaching process, experimental results show that when the concentration of TBCC (N-4-(triethylammoniummethylenebenzoyl)caprolactam chloride) is increased to the range of 25-100 g/L, the bleaching effect is unexpectedly weakened; dynamic adsorption experiments show that this is likely due to the relatively high TBCC concentration, and because the adsorption of TBCC and peroxy acid on cotton fabrics increases, the peroxyacid activity is relatively low, thus limiting the bleaching efficiency; such limitation is particularly fatal in the cotton fabric cold pad-batch bleaching process that requires high concentrations of TBCC.
Therefore, there is a need to improve the bleaching process to overcome the problems of unstable bleaching effect of the TBLC-activated hydrogen peroxide system and long time required for a cold pad-batch implementation process in the cold pad-batch bleaching process which currently requires higher concentrations of chemicals.